1. Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More specifically, the present invention relates to diffusers in plasma processing systems.
2. Description of the Related Art
Semiconductor processing systems are used to process semiconductor wafers for fabrication of integrated circuits. In particular, plasma-based semiconductor processes are commonly used in etching, oxidation, chemical vapor deposition (CVD), etc. Conventional plasma processing systems typically control gas or plasma flow in a plasma processing chamber to provide an optimum environment for processing the wafer.
In addition, these systems generally include other chambers for handling and transporting wafers between atmosphere and vacuum to ensure a clean process environment. To process a wafer, for example, the wafer in atmosphere is transported to a wafer load lock, which is a chamber that cycles between vacuum and atmosphere. When the wafer is placed in the wafer load lock, the load lock will contain atmosphere. The air in the atmosphere is then pumped out to provide a vacuum condition in the load lock chamber. The wafer is then transported to the processing chamber by a robotic arm operating in a vacuum chamber. The processing chamber processes (e.g., etching, oxidation, CVD, etc.) the wafer by exposing it to gas or plasma, which are pumped into and out of the chamber. This process changes the characteristics of the wafer.
After the wafer has been processed, the robotic arm in the vacuum transfer module moves the wafer back to the load lock in vacuum condition. Once the wafer is placed in the load lock, the vacuum pressure in the load lock is changed back to atmospheric pressure by flowing in a gas such as N2. When atmospheric pressure has been achieved, the wafer is transported to a wafer cassette for other processing steps, if necessary.
In semiconductor processing, the value of a process system depends to a large extent on the rate at which wafers can be processed. That is, a process system with higher process rate will produce more processed wafers in a given amount of time than a system with lower process rate. Thus, the greater the process rate, the more valuable a process system is due to the greater throughput.
In conventional semiconductor process systems, however, the process rate of wafers depends largely on the speed with which chambers such as load lock, vacuum transfer module, and process chamber can be cycled between low and high pressure states. Unfortunately, the cycle speed of a chamber in conventional process systems is generally limited in practice by the maximum local velocity of the in-coming gas and outgoing gases. For example, too high a velocity may move the wafer out of position. Further, if the maximum velocity of the gases is too high, the gases may entrain small particles in the vacuum chamber and redistribute some of them onto the wafer surface. As can be appreciated, particulate surface contaminants may lead to failures of integrated circuits made from such wafer. To prevent such failures, therefore, the local velocity needs to be maintained below a certain level.
To address such problems, conventional chambers often include diffusers to slow the incoming gas flow by spreading the flow evenly over a wider area in the chambers. To provide such functions, a diffuser is typically equipped with a membrane provided at the chamber interface. The membrane typically consists of fabric, sintered metal, or a plate with many small holes in it. In this configuration, a cavity behind the membrane serves to spread the flow over a wider area. The membrane provides a resistance to the flow. This resistance allows the pressure to equalize behind the membrane. The uniform pressure and the uniform membrane resistance provide a uniform flow.
However, conventional diffusers equipped with membranes have several drawbacks. For example, such diffusers tend to be expensive because they need to retain substantial pressure. Typically, several pounds of pressure across the membrane are required. The membrane thus needs to be strong enough to withstand the pressure and yet allow gas to flow uniformly through, thereby adding to the cost of diffusers or limiting the speed of the venting portion of the cycle. Further, during the pumping part of the cycle, the membrane may hinder gas flow, thereby slowing down the pump cycle. In addition, the small holes in the membranes may trap minute particles during venting and/or pumping cycles. Due to these particles, the pumping and venting efficiencies may degrade over time or the particles may be released into the vent flow and land on the wafer surface. In addition, the membranes in the diffusers may be difficult to clean.
In view of the foregoing, what is desirable is a diffuser which an provide the required large area and low velocity flow in both pump and vent parts of the cycle with low resistance to the flows. This will allow an increase in the wafer process rate. In addition, a diffuser through which both pumping and venting can take place will be an advantage because of cost savings and/or the ability to fit a larger diffuser with the available space.
Broadly speaking, the present invention fills these needs by providing a diffuser and a rapid cycle chamber for venting and/or pumping gas. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In accordance with one embodiment, the present invention provides a diffuser that includes a body and a reflector. The body includes a nozzle through a center portion and has a curved surface on an upper side to define an open space above the curved surface. The nozzle is arranged to allow a gas to flow through and expand in the nozzle. The reflector is disposed over the nozzle and is arranged to reflect the gas from the nozzle into the open space in the body while expanding the gas flow. In this configuration, the flow of the gas is slowed in the nozzle, the reflector portion, and the open space in the body so that the gas flows out of the open space with low velocity.
In another embodiment, the present invention provides a chamber for cycling gas in a semiconductor processing system. The chamber includes a set of enclosed walls and a diffuser. The diffuser is mounted in an aperture in an enclosed wall of the chamber. The diffuser includes a body, a reflector, and a set of vanes. The body includes a nozzle through a center portion and has a curved surface on an upper side to define an open space above the curved surface. The nozzle is arranged to allow a gas to flow through and expand the gas flow. The reflector is disposed over the nozzle and is arranged to reflect the gas from the nozzle into the open space in the body while expanding the gas flow. In this configuration, the flow of the gas expands and slows in the nozzle, the reflector, and the open space into the chamber with low velocity. The set of vanes is disposed in the open space of the body for partitioning the open space into a set of expansion spaces such that the gas flows out of each expansion space in substantially equal amounts from the partitioned spaces into the chamber. The number and shape of the vanes are chosen to provide a substantially uniform flow out of the open space into the chamber.
In yet another embodiment, a flow restrictor is disposed on the inlet to limit the velocity of an input gas. In one embodiment, a separate sonic flow restrictor may be utilized to limit the gas flow into the nozzle to slow the gas flow and prevent a burst of gas flow into the nozzle when the upstream valve is opened.
The present invention provides substantial advantages over conventional diffusers. For example, the diffuser of the present invention may be used to vent gas into a chamber or pump the gas out of a chamber. When used in venting, for example, the nozzle, reflector, and expansion hollow expand the incoming gas flow gradually in a small height. Due to the low and uniform gas flow into the chamber, wafers in the chamber will not be moved out of position. In addition, minute particles within the chamber are less likely to be entrained in the flow and deposited onto a wafer in the chamber. Accordingly, the diffuser and chamber equipped with such a diffuser of the present invention increase wafer throughput and/or device yield in a semiconductor processing system. On the other hand, the diffuser may also be used to pump the chamber to vacuum. By using the diffuser in this mode, the chamber need not employ a separate pumping port or device, thereby saving space in the chamber or allowing a larger diffuser to be employed. These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.